A Preliminary Investigation Into the Use of Edible Fishery By-products as Sources of Nutrients for Fish and Livestock Feeds on Zanzibar, Tanzania

Abstract

A survey, to measure the quantity of edible fish waste (gills and guts) available per year, was conducted on Unguja Island, Zanzibar between December 2003 and February 2004. Seventeen samples from commercially important fish genera and species were collected from five landing sites (‘dikos’) in five districts of the Island, dissected and the amount of wastes quantified as percentage of individual body weights. Reliable data on annual catches (tonnage) of the selected species or genera were used to extrapolate total amounts of fish waste produced. Separate samples (gills and guts) were isolated and treated as (1) boiled and sun dried and (2) sun dried without boiling; and analyzed to determine fat (EE g/100gDM), mineral (ash g/100gDM) and protein (CPg/100gDM). In addition, bulky fish wastes (mixed gills+guts) were collected from the same sites, boiled, sun dried and stored for further feeding trials and duplicate samples analyzed. Results show percentage fish waste (%Ww) between individual genera and species varied significantly (10.47±0.93; P<0.001). Average annual fish waste produced is 2.040t out of total 1.84, 1.81, 1.79 and 2.72 thousand tonnes from the years 2001, 2002, 2003 and 2004 catches respectively. The body parts of fish significantly determined fat and mineral composition (LSM for gills = 10.85±1.486 g/100gDM EE vs. guts = 15.45±1.486 g/100gDM EE; P = 0.033 and LSM for gills = 23.49±1.494 g/100gDM mineral vs. guts = 14.27±1.494 g/100gDM Ash; P<0.001), while treatment (boiling at 95 - 1050C) had no effect on both fat, protein and mineral. Significant variation in overall protein content between species (LSM = 57.68±2.33; P<0.001) is observed. Slight dispersions between sites for mineral (LSM = 29.1±2.01 g/100gDM) and fat (LSM = 13.93±1.05 g/100g DM) showed up in bulky wastes. It was concluded that valuable quantity of fish waste is available to reduce the limiting protein supplementation problem in both livestock and fish farming in the western Indian Ocean region. However, additional on-station and on-farm studies are required to measure the intakes and effects of the supplement on milk yields and growth performances.